Coding Variation in ANGPTL4, LPL, and SVEP1 and the Risk of Coronary Disease

Background

Several lines of evidence point towards a causal role for serum triglycerides (TGs) in the risk of CV disease, including Mendelian randomisation studies [1]. Other genetic evidence that supports a causal relationship includes the observation that APOC3 inactivating mutations were associated with lower TG levels, decreased burden of subclinical atherosclerosis, and a lower risk of ischemic CV disease [2-4].
Lipoprotein lipase (LPL) is the main enzyme that hydrolyses lipoprotein TGs, thereby releasing free fatty acids. Mutations that increase LPL activity lower serum TG levels and the risk of CV disease and mutations that lower LPL function lead to higher serum TG levels [5,6]. Angiopoietin-like 3 (ANGPTL3) and angiopoietin- like 4 (ANGPTL4) are two proteins that inhibit LPL. Angptl4-deficient mice show smaller atherosclerotic lesions [7].
The amino acid–altering (missense) E40K variant in human ANGPTL4 has been associated with lower TG levels and higher HDL-c [8]. Some conflicting results have been published on the association of this variant with the risk of coronary artery disease (CAD).
This study by Dewey et al. examined associations between the presence of the E40K variant and lipid levels and CAD, as well as associations of novel, rare, inactivating mutations in ANGPTL4 (in 42930 participants of the DiscovEHR study). Moreover, therapeutic inhibition of Angptl4 was evaluated in murine and nonhuman primate models.

Dewey et al. - Main results

1661 out of 42390 (3.9%) DiscovEHR participants were heterozygous for the E40K mutation, and 17 (0.04%) were homozygous. 13 other distinct mutations were identified that were predicted to inactivate ANGPTL4 (75 individuals were heterozygous for one of these).

TG levels were 13% lower per allele among carriers of the E40K variant, than among E40 homozygotes and HDL-c levels were 7% higher in E40K carriers than in E40 homozygotes (normal allele).
Carriers of inactivating mutations other than the E40K variant showed similarly lower TG levels (13%) and 9% higher HDL-c than noncarriers.

The E40K variant was less common among participants with CAD (357 heterozygotes and 2 homozygotes in 10552 cases, allele frequency: 1.7%) than among controls (1196 heterozygotes and 15 homozygotes, allele frequency: 2.1%). The risk of CAD decreased with 19% per E40K allele (OR: 0.81, 95%CI: 0.70-0.92, P=0.002).
The cumulative allele frequency of newly identified inactivating mutations in ANGPTL4 were also lower in CAD patients than in controls (0.06% vs. 0.1% in controls).
Overall, the presence of an inactivating mutation yielded a 44% lower odds of CAD (OR: 0.56, 95%CI: 0.32-1.00, P=0.05).

Cynomolgus monkeys on a high-fat diet receiving the Angptl4-antibody showed lower levels of serum TGs than control monkeys.

The simultaneously published DNA sequencing study by the Myocardial Infarction Genetics and CARDIoGRAM Exome Consortia Investigators examined the presence of over 54000 coding-sequence variants in up to 72868 patients with CAD and 120770 controls without CAD.

Among 6924 patients with MI, 9 carriers of loss-of-function (LOF) ANGTPL4 were identified, and 19 carriers were seen among 6834 controls (OR: 0.47, P=0.04).

Carriers of LOF ANGTPL4 alleles had 35% lower TG levels than persons who do not carry a LOF variant (P=0.003).

An LPL LOF variant was identified, which was associated with an increased risk of CAD (p.D36N: minor-allele frequency: 1.9%, OR: 1.13, P=2.0x10-4) and a gain-of-function variant was associated with protection from CAD (p.S447*: minor-allele frequency, 9.9%, OR: 0.94, P=2.5x10-7).

Conclusion

The study by Dewey et al revealed that inactivating gene variants of the ANGPTL4 gene, which prevent the normal inhibitory effect of ANGPTL4 on LPL, were associated with lower serum TG lipid levels and increased HDL-c levels, as compared with homozygotes of the most common allele. Lipid levels in the small group of E40K homozygotes suggests a gene-dosage effect of the variant. Moreover, inhibition of ANGPTL4 with an antibody in mice and monkeys lowered TG levels.
The study by the Myocardial Infarction Genetics and CARDIoGRAM Exome Consortia Investigators also revealed an association of the coding variant in ANGPTL4 with protection against CAD and they show evidence that LPL contributes to the risk of CAD, such that LPL gain of function may protect against disease.
Together, these data suggest that modulation of ANGPTL4 affects TG metabolism and the LPL pathway, in that loss of ANGPTL4 function lowers CAD risk through lowering TG levels.

Editorial comment [9]

These two studies provide convincing evidence that an elevated plasma TG level increases the risk of CAD. “The new findings also implicate targeted inactivation of ANGPTL4 as a potential weapon in thewar on heart disease.” But the E40K variant has also been associated with an increased risk of CHD after adjustment for altered plasma levels. Thus, the variant may also have a CHD stimulating effect independent of plasma lipids. The effectiveness of targeting ANGPTL4 to reduce plasma TG levels was tested in the study by Dewey et al., by injecting mice and monkeys with an anti-Angptl4 antibody. While regular injections lowered plasma TG levels, enlarged mesenteric lymph nodes were observed. “Although carriers of ANGPTL4 mutations did not seem to be more affected by abdominal lymphatic disorders and related intestinal diseases than were controls, these observations raise concern about the safety of targeting ANGPTL4.It is unfortunate that the investigators did not measure plasma levels of serum amyloid or another acute-phase protein in the monkeys or in human mutation carriers.” (…) “These two studies that identify ANGPTL4 as a link between triglycerides and coronary heart disease not only improve our understanding of elevated triglyceride levels in heart disease but also provide a path to the development of future therapies for dyslipidemia.”